The 28-year-old midfielder joins on a two-year deal after his spell at Huish Park came to an end, and follows Remi Streete and Sam Kelly through the door at the Valiants.
The former Ireland youth international was a regular last season, making 45 appearances as Yeovil suffered relegation to League Two, but he subsequently turned down the offer of a new deal at Huish Park.
Instead, he has opted to join Port Vale, and manager Rob Page told the club’s official website he would be a good addition to the squad.
He said: “We are delighted to have Sam on board after winning the race to secure his signature.
“He’s an experienced player who is very intelligent in his approach to the game and I’m sure the lads will enjoy lining up alongside him next season.”